For many years, switches were considered simplistic devices with the crudest of parametric characteristics. However, applications for switches, such as snap-acting switches, are becoming more exacting and, accordingly, switch users and makers are requiring more precise and accurate switches. Thus, more stringent quality control procedures and manufacturing standards are being implemented both to produce switches which can be used in these more exacting applications and to increase the manufacturing productivity of these switches.
A typical snap-acting switch has a movable contact actuated between a normally closed position and a normally open position upon movement of a switch plunger. Such a switch has an operate point or operating position, which is the point along a displacement axis with respect to a reference point at which the movable contact of the switch transfers from one of its positions (i.e., the starting position) to the other of its positions, and a reset point, which is the point along the displacement axis with respect to the reference point at which movable contact of the switch transfers back to its starting position.
In precision measuring operations, it is imperative to know the precise location of the operate and reset points along with other switch and plunger characteristics such as switch contact resistances, plunger force characteristics, and plunger travel characteristics. Thus, when manufacturing switches, it is important to assure that the switch, as manufactured, falls within required customer specifications for each of the switch characteristics. To do this in a simple, quick and efficient manner, a switch test station which automatically tests for each of the desired switch characteristics and determines if the switch falls within predetermined specifications is required.
An example of a known test station is disclosed in Terminiello, et al., U.S. Pat. No. 5,117,189 which describes a computer controlled test station which automatically loads a switch into an activating position and applies pressure to the switch plunger to thereby actuate the switch. This test station measures the movement hysteresis of the switch, i.e., the relative distance between the displacement of the switch plunger when the movable contact of the switch is at the operate point of the switch and the displacement of the switch plunger when the movable contact of the switch is at the reset point. This test station also measures switch deadbreak, i.e., the amount of time it takes the movable contact of the switch to move between the normally closed and the normally open positions. The test station then sorts the switches into separate bins according to the results of the two tests described above.
Single test, switch testing devices are also known. An example of such a device is described in Jay, U.S. Pat. No. 4,854,165. The device disclosed therein tests pneumatically actuated switches in order to determine the exact amount of fluid pressure needed to actuate the switch. Another single test, switch testing device, shown in Velsher, U.S. Pat. No. 4,491,797, includes a test circuit for precisely measuring the contact resistance of dry circuit contacts. This test circuit supplies a precise current through the switch contacts while measuring the voltage across the contacts so as to determine the contact resistance.
No one of these known switch test devices is capable of measuring the many switch characteristics which are required for switches used in current applications. Moreover, none of these known switch test devices measures these plural switch characteristics during a single switch actuation cycle. Furthermore, presently known test devices cannot universally test different types of switches, but rather are dedicated to only a specific switch type. Known switch test devices cannot test all channels of a multiple channel switch during a single switch actuation cycle and are imprecise.